The invention relates to a thermoplastic elastomer composition, comprising
a) from 5 to 99% by weight of a block copolymer which is composed of hard blocks S made from vinyl aromatic monomers and of one or more random soft blocks B/S made from dienes and from vinyl aromatic monomers,
b) from 1 to 95% by weight of a plasticizer with a higher polarity than white oil and with a lower polarity than dioctyl phthalate,
c) from 0 to 50% by weight of a polyolefin, and
d) from 0 to 60% by weight of additives,
where the total of a) to d) is 100% by weight.
The invention further relates to the use of the molding compositions for producing flexible or elastic moldings, and also to the resultant moldings.
Thermoplastic elastomer compositions based on hydrogenated or nonhydrogenated styrene-butadiene or styrene isoprene block copolymers (S-TPE) and, if desired, on polyolefins are known (e.g.: EP-A 0 583 228, EP-A 0 623 651, EP A 0 712 892 or EP-A 0 845 498). The physical properties, such as elasticity, hardness, tensile strength or adhesion, can be adjusted over a wide range via the selection of the auxiliaries and via the mixing ratios. The plasticizers used usually comprise low-aromatic paraffinic oils, naphthenic oils or oligomeric polybutadienes.
Thermoplastc elastomers or elastomer compositions based on block copolymers made from styrene and butadiene, with one or more random soft blocks B/S, are known from WO 95/35335 and WO 96/20248. Compared with thermoplastic elastomers with a soft phase made from a pure butadiene block, they have better processability, better weathering resistance, better thermal melt stability and better printability and paintability, e.g. with surface coatings.
The relatively high polarity of the soft blocks B/S means that these block copolymers have only limited compatibility with white oil, which is usually used as plasticizer for traditional S-TPEs.
It is an object of the present invention to provide a thermoplastic elastomer composition which does not have the abovementioned disadvantages and which, in particular when use is made of block copolymers with random soft blocks B/S, can be adjusted to any desired hardness without bleed-out of the plasticizer.
We have found that this object is achieved by means of the abovementioned thermoplastic elastomer composition.
The thermoplastic elastomer composition comprises from 5 to 99% by weight, preferably from 49 to 94% by weight, of a block copolymer which is composed of hard blocks S made from vinyl aromatic monomers and of one or more random soft blocks B/S made from dienes and from vinyl aromatic monomers.
Suitable vinyl aromatic monomers for the hard blocks S and also for the random soft blocks B/S are styrene, xcex1-methyl styrene, vinyl toluene or mixtures of these.
The dienes used may comprise butadiene, isoprene, piperylene, 1-phenylbutadiene or mixtures of these.
Particular preference is given to block copolymers made from styrene and butadiene.
The preparation and properties of block polymers of this type are described, for example, in WO 95/35335 or WO 97/40079. They can be obtained by anionic polymerisation in a nonpolar solvent with addition of a polar cosolvent or of a potassium salt.
The morphology which results from the incompatibility of the blocks S and B/S is important in determining the suitability of the block copolymers as thermoplastic elastomers. The blocks B/S aggregate in the soft phase which forms the continuous matrix and are responsible for the elastomeric behavior at the service temperature. The blocks S are predominantly in the form of isolated, mostly bead-shaped, inclusions, which act as physical crosslinking points.
Symmetrical three-block copolymers and star-block copolymers with outer blocks S and with one or more blocks B/S lying therebetween are particularly suitable as thermoplastic elastomers.
The block copolymer preferably has a diene content of less than 50% by weight, preferably from 15 to 50% by weight, particularly preferably from 25 to 40% by weight, based on the entire block copolymer.
The proportion of the soft phase formed from the blocks B/S is generally at least 60% by weight, preferably from 60 to 80% by weight, particularly preferably from 65 to 75% by weight, based on the entire block copolymer. The blocks S formed from the vinyl aromatic monomers form the hard phase, the proportion of which is not more than 40% by weight, preferably from 20 to 40% by weight, particularly preferably from 25 to 35% by weight.
The random structure of the soft blocks B/S means that the glass transition temperature is generally from xe2x88x9250 to +25xc2x0 C., preferably from xe2x88x9250 to +5xc2x0 C., particularly preferably from xe2x88x9250 to xe2x88x9215xc2x0 C. The glass transition temperature of the hard block S is preferably above 25xc2x0 C., particularly preferably above 50xc2x0 C.
The soft block B/S is preferably composed of from 30 to 75% by weight, particularly preferably from 30 to 65% by weight, of vinyl aromatic monomer, and from 25 to 70% by weight of diene, particularly preferably from 35 to 70% by weight. The soft block B/S may have been subdivided into two or more random soft blocks with different molecular weights or different monomer compositions.
The molar masses of soft block B/S is usually from 2,000 to 250,000, preferably from 20,000 to 150,000, particularly preferably from 60,000 to 120,000 [g/mol].
The molar mass of a block S is generally from 1,000 to 200,000, preferably from 5,000 to 50,000, particularly preferably from 15,000 to 25,000 [g/mol]. The block copolymer may be composed of blocks S with identical or different molar masses.
The block copolymers are usually mixed with stabilisers. Examples of suitable stabilizers are stearically hindered phenols such as Irganox(copyright) 1076 or Irganox(copyright) 3052 from Ciba-Geigy, Basle or xcex1-tocopherol (Vitamin E).
The thermoplastic elastomer composition also comprises from 1 to 95% by weight, preferably from 4 to 49% by weight, of a plasticizer with a higher polarity than white oil and with a lower polarity than diisooctylphthalate. Particular preference is given to the use of plasticizers which are only slightly more polar than white oil. Examples of suitable plasticizers are substances which have polar groups, such as ester, amide, ether, and also an aliphatic radical having 12 to 18 carbon atoms. Examples of these are naturally occurring or synthetic esters of fatty acids, amides of fatty acids or esters of fatty alcohols. Preferred esters of fatty alcohols are those of citric acid, adipic acid or other di- or oligocarboxylic acids. The plasticizers mentioned may be used individually or in mixtures. It is also possible to use mixtures with paraffinic or naphthenic oils. The best mechanical properties are obtained by using a mixture of a plasticizers with white oil, where the amount of white oil used is just that required to avoid any separation out from the block copolymer.
Reference is given to the use of plasticizers comprising vegetable oils, such as sunflower oil, or comprising a mixture of vegetable oils and white oil.
The hardness and flowability of the thermoplastic elastomer composition may be varied over a white range via the amount of the plasticizer used.
The thermoplastic elastomer composition may comprise from 0 to 50% by weight, preferably from 1 to 30% by weight, of polyolefins, such as polyethylene, polypropylene, polybutylene, polyisobutylene, ethylene-propylene rubbers, or also EPDM rubbers. Preference is given to the use of metallocene polyethylene with a narrow molecular weight distribution and polyolefins with a high crystalline melting point, such as polypropylene. Soft polyolefins may be used to improve resistance to certain media, for example oils and solvent, and also to improve the tear propagation resistance of the elastomer composition, and crystalline polyolefins may be used to improve heat resistance and compression set.
Other components which may be present in the elastomer composition are additives of any type, usually in amounts of from 0 to 60% by weight, preferably from 1 to 40% by weight, based on the elastomer composition. Examples of possible additives are fibrous or pulverulent fillers, fibrous or pulverulent reinforcing materials, stabilisers, flame retardants, pigments, dyes, and processing aids, such as lubricants and mold-release agents. Preference is given to the use of inorganic fillers, such as talc, carbonates, sulfates, oxides of varying hydration levels, in particular titanium dioxide, Ca silicates, Mg silicates, silicates such as Aerosil, silica gel or kieselguhr, or carbon black. Substantially transparent mixtures can be obtained by adding nanocomposites. These are phyllosilicates, such as montmorillonite, which have preferably been impregnated with hydrophobicizers, such as amines or salts with quaternized amines.
The novel molding compositions may be obtained by mixing and homogenizing the components by the usual methods of plastics technology, and the sequence of adding the components may be varied. Examples of suitable mixing equipment are continuous or batch kneaders, Banbury mixers, or co-rotating or counter rotating single- or twin-screw extruders.
The novel elastomer composition is elastic, can be processed as a thermoplastic, and can readily be recycled by remelting. The novel elastomer composition is recommended for two-component (2C) injection molding, since it has excellent processability and compatibility with thermoplastics based on styrene, such as glass-clear polystyrene (GPPS), impact-modified polystyrene (HIPS), styrene-butadiene block copolymers, such as Styrolux(copyright) from BASF Aktiengesellschaft or K-Resins(copyright) (Phillips), and styreneacrylonitrile polymers (SAN) and acrylonitrile, and with butadiene styrene polymers (ABS) polyphenylene ethers. The interface between the hard component and the novel elastomer composition as soft component is, furthermore, transparent. Using 2C injection molding in this way it is possible to produce flexible and rigid parts in a single casting. Other possible hard components are polyesters and polycarbonate.
The novel elastomer composition may readily be painted or printed, even without corona treatment. It is therefore suitable for producing elastic or flexible moldings, such as toys, parts for toys, xe2x80x9csoft-touchxe2x80x9d applications, such as grips or antislip surfaces, gaskets, switches, housings with sealing lips, control knobs, flexographic printing plates, shoe soles, hoses, profiles, medical items, such as infusion kits, dialysis units and breathing masks, hygiene items, such as toothbrushes, materials for insulating or sheathing cables, sound-deadening elements, folding bellows, rolls or roll coatings, and carpet backings.